Masks and filters are worn over the head or face in order to protect individuals from exposure to toxic chemical vapors. In these devices, there is no convenient or effective way to tell whether the adsorbent in the mask is fresh or used. A sensor which could fit inside the protective sorbent bed and indicate the remaining useful lifetime of the filter would be ideal. In this work, a micropower microsensor has been designed and fabricated. This sensor can fit inside a carbon adsorbent bed and determine whether the filter is operating properly or whether it is exhausted and hazardous vapors are penetrating the protective device. Laboratory and field tests of the new microsensor will culminate in a new product which will alert mask users to hazardous conditions resulting from the depletion of protective sorbent filters.